Decoupling alkali and alkaline-earth oxide effects on pyroplastic deformation in porcelain tiles via engineered frits

Pyroplastic deformation, defined as the loss of dimensional stability during firing, remains a critical challenge in porcelain tile manufacturing, particularly for large-format products requiring simultaneous densification and shape retention. Conventional studies have assessed the influence of alkaline and alkaline–earth oxides by adjusting fluxing raw materials such as feldspars; however, this strategy inevitably alters SiO 2 and Al 2 O 3 contents, masking the individual contributions of fluxing oxides. Here, we introduce a novel methodological approach based on engineered ceramic frits with compositionally controlled fluxing fractions, enabling to evaluate the effect of Na 2 O, K 2 O, CaO, and MgO oxides on pyroplasticity. By using optical fleximetry, X–ray diffractometry with Rietveld refinement, microstructural analysis, and physical characterization, we systematically quantified the roles of these oxides in liquid–phase formation, viscosity, densification, and dimensional stability. Among the tested formulations, composition C4.2 (61.4 wt% clays, 2.1 wt% talc, and 36.5 wt% frit F4) exhibited the most favorable balance, combining low water absorption (0.38 ± 0.02%), moderated linear shrinkage (6.8 ± 0.1%), high flexural strength (45 ± 2 MPa), and reduced pyroplastic deformation index (7.8 ± 0.2 × 10 −5 cm −1 ) when compared with an industrial reference (benchmark) formulation. These findings demonstrate that tailoring frit chemistry provides a mechanistic framework for resolving long–standing ambiguities regarding the isolated effect of alkaline and alkaline–earth oxides. Beyond mechanistic insight, this approach establishes a transferable design strategy that bridges oxide–level control with industrial translation, enabling the development of optimized, dimensionally stable porcelain tiles. • A novel methodological approach based on engineered ceramic frits is presented. • Compositionally controlled fluxing fractions for understanding pyroplasticity. • We studied alkaline and alkaline–earth oxide effects on pyroplasticity of porcelain. • This approach favours the development of optimized, dimensionally stable porcelains.